The long term goal of this proposal is to define the cellular and molecular mechanisms underlying the myelination defect of the free sialic acid storage disorders (FSASDs) in order to lay the foundation for novel therapeutic approaches. The FSASDs are one group of inherited lysosomal storage disorders caused by mutations in the gene that encodes sialin and manifest in children as neurodevelopmental defects. Sialin, a sialic acid transporter, localizes to the lysosomal membrane and pumps sialic acid out of the lysosome after it has been cleaved from glycoproteins and glycolipids undergoing degradation. Both human patients and a mouse model of the FSASDs manifest a pronounced hypomyelination of the central nervous system (CNS). This proposal aims to test the hypothesis that loss of sialin leads to improper metabolism of sialic acid- bearing glycoconjugates required for myelinogenesis. The first aim is to determine whether myelin formation or maintenance is affected in the sialin-/- mouse using Western blotting and electron microscopy on mouse nervous tissue. The second aim is to determine the cellular mechanisms of hypomyelination in the sialin-/- mouse. Immunofluorescence studies on complementary in vitro neuronal-glial coculture and in vivo systems will be used to determine whether the hypomyelination is caused by a decrease in numbers of myelinating oligodendrocytes or a defect in axonal-oligodendroglial signaling required to produce compact myelin. The third aim is to identify changes in CNS sialoglycoconjugate expression in the sialin-/- mouse. Metabolism of sialylated proteins and lipids critical for myelin formation is likely affected by loss of sialin function and may be a primary mechanism responsible for the developmental defect. Overall expression levels of sialoglycoconjugates will be determined using an enzymatic method and changes in specific sialoglycoconjugates will be identified using thin layer chromatography and Western blotting. These aims will lead to an improved understanding of how sialin function influences development of the nervous system and how loss of function leads to disease. PUBLIC HEALTH RELEVANCE: The free sialic acid storage disorders (FSASDs) are inherited diseases that cause neurodevelopmental defects and premature death by disrupting normal function of the lysosome, an organelle that serves as the recycling center of the cell. The goal of the proposed experiments is to determine how loss of sialin, the lysosomal protein affected in the FSASDs, leads to abnormal development of the brain. A better understanding of this will be a critical first step toward developing novel approaches to treat these and related disorders.